The symbiotic relationship between intestinal microbiota and the host plays an important role in the intestinal development. Interruption of this relationship leads to infectious and immune-mediated diseases. This underscores the importance of identifying the effects of probiotics on intestinal development and disease prevention in children. However, there are critical gaps in knowledge about mechanisms of probiotic action. The efficacy of probiotics for nutritional and clinical application remains to be convincingly established. p40, a LGG-derived protein isolated and cloned by our group, activates epidermal growth factor receptor (EGFR) and its downstream target, PI3K/Akt in intestinal epithelial cells through stimulation of EGFR ligand release. Activation of EGFR by p40 is required for inhibition of cytokine-induced apoptosis, preservation of barrier function, and enhancement of mucin production in intestinal epithelial cells. We have generated a pectin/zein hydrogel bead system to specifically delivered p40 to the colon in mouse. By using this delivery system p40 has been sown to prevent and treat experimental colitis in mice in an EGFR-dependent manner. Since activation of EGFR plays a physiological role in development, we have expanded the scope of our work to investigate the effects of p40 on intestinal development. Based on our preliminary results that LGG colonization promotes functional maturation of the intestine and decreases susceptibility to intestinal injury and colitis in adult mice, three integrated specific aims are proposed to enhance knowledge of the functional nature of p40 in regulation of intestinal development and mechanisms of the action of p40. In Specific Aim 1, the roles of p40 in intestinal functional maturation will be determined. We will use neonatal mice, human fetal intestinal organ culture, and human and mouse enteroids to determine the roles of p40 in intestinal epithelial cell proliferation, differentiation, migration,and digestive and absorptive capacities and epithelial tight junction formation. In Specific Aim 2, transcriptional targets in intestinal epithelial cells involved in p40-regulated cellular responsesto promote intestinal functional maturation will be defined. We will determine p40-regulated intestinal epithelial genes in neonatal mice and in human fetal intestinal organ culture, and verif the function of individual candidate p40-regulated genes predicted to regulate epithelial proliferation, differentiation, migration, transporters, and tight junction formation using in vitr and ex vivo assays. In Specific Aim 3, the p40- stimulated signaling pathway in intestinal epithelial cells that is required for promotion of intestinal functional maturation will be elucidaed. We will use mouse models with intestinal epithelial cell-specific deficiency of EGFR and PI3K and pharmacologic inhibition of EGFR and Akt in human fetal intestinal organ culture and enteroids to determine the requirement of EGFR and Akt activation for p40-stimulated epithelial responses and p40-regulated EGFR and Akt-dependent transcriptional targets for functional maturation. These studies will contribute new information for nutritional and clinical applications of p40 for health in children.